Hi. I'll skip most of the equipment recommendations; were I buying fresh now, I'd either get a Shearwater Teric (I like rechargeable) or Perdix A.I. (some like swappable batteries you don't have to recharge), and I like air-integration so my computer logs start & end pressures and uploads to my computer, giving me SAC rate, average in addition to max. depth, and minimum temp. - and shows if I had a smooth vs. sawtooth profile. Oh, and for us big-footed folks, Deep 6 Eddy fins are sweet, and bring slightly positively buoyant, a nice choice for us 'foot heavy' folks (which a lot of wetsuit divers tend to be, I think).
I agree you'll want the nitrox cert.
If you want a whole lot of diving, Bonaire with a lot of shore diving, or a live-aboard, or a destination with an op that offers more than 2 mornings dives/day is the way to go.
Tres Pelicanos in Cozumel and
Rainbow Reef Dive Center in Key Largo both let me get in 4 per day. At Little Cayman Beach Resort or Cayman Brac Beach Resort I think you can get 3 dives/day, and maybe a couple night dives offered for the week. CocoView Resort in Roatan will do 'drop off' dives on the way back from boat trips, so you can fin back to the house reef and exit on shore, plus you can do shore dives. There are others.
Shore diving in Bonaire would let you go at your own pace without having to keep up with a guide, group and boat's time limit dictate. You can dive over sand bottom in places to reduce risk of causing reef damage while you practive skills. The island is big enough to be interesting, small enough not to be overwhelming, and at some point you'll want to try shore diving.
My Research Notes for Bonaire -
My Research Note For Bonaire Honorable mention for a larger alternative with more sandy beaches and topside stuff -
Curacao Trip Research Notes
Curacao Trip Report with SB Surge Jan. 2019
There are many options for 1st live-board trips; I started out with the
Sun Dancer 2 (now called
Belize Aggressor IV), and later did the
Cayman Aggressor IV (there's now a V out instead, larger). Here's
a thread on picking a 1st Caribbean Live-aboard.
Any weight and trim dialing in you do in a cold lake will be off when you hit the tropics with a lot less exposure protection, but the experience will be useful should you later try
diving California (cold, lower average viz. than some places, but really nice Channel Islands diving and has things you won't see in the Caribbean).
If you want the short version, here's what I suggest. Go to Bonaire. Focus on shore diving, get whatever skills practice and tropical conditions weighting/trim dialed in to suit yourselves and sense of how you dive in such. Yeah, visit the Donkey Sanctuary, spend a half-day driving through the park up north and take photos, but for the most part, 'dive the crap out of it.'
If that goes well, follow up with a high dive count trip. Key Largo, a live-aboard, LCBR, CBBR, CocoView Resort, and of those would do. I might save Cozumel till your next trip, as drift diving is a bit different, but let's be clear, Coz. rocks!
After that, you can consider whether you want to see big animals, lots of wrecks, visit kelp forests or otherwise get away from the 'underwater flower gardens' of coral reefs, go see something different.